DESCRIPTION (Adapted from Applicants' Abstract): The epithelial lining of the mammalian intestinal tract develops from a simple tube of embryonic endoderm through a complex process of changes in morphology and gene expression. However, little is known about the molecular mechanisms that direct and integrate the developmental transitions leading to the mature configuration of the adult intestinal epithelium. Using expression cloning, the applicant has identified a cDNA encoding a protein that binds with high affinity to, and activates transcription of, an intestine-specific DNA regulatory element. The protein encoded by this cDNA is a member of the caudal-related homeodomain family of transcription factors (Cdx): homeodomain proteins are central importance in may organisms for developmental processes throughout embryogenesis and organogenesis. This proposal is based on the hypothesis that Cdx genes are important for directing development and differentiation of the mouse intestinal epithelim. Therefore, the overall goal of this application is to investigate the role of Cdx genes in intestinal organogenesis and differentiation. To achieve this goal, the first aim is to clone members of the Cdx family of homeodomain genes that are expressed during intestinal developmental and to characterize their temporal and cellular patterns of expression. The clonings will be achieved by Rapid Amplification of cDNA Ends (RACE) procedure using RNA from developing small intestine and colon and the patterns of expression examined in the developing intestinal tract using in situ hybridization and immunohistochemistry.The second aim is to examine the functional role of Cdx genes in differentiation of the intestinal epithelium using intestinal cell lines. Several cell lines that have been derived from intestinal tissue or colon carcinomas, as the gain of function and loss of function of Cdx genes. The third aim is to examine the functional role of Cdx genes ind development of digestive tract using the transgenic mice. Gain of function and loss of function studies will be performed in transgenic mice using the promoter of the villin gene to express constructs that contain coding regions for Cdx genes and the effect on development will be evaluated. The strategy will allow an assessment of the effect of premature and ectopic expression of Cdx genes in the intact mouse.